305-300 Practice Exam Questions with Answers LPIC-3: Virtualization and Containerization - Exam 305, version 3.0 Certification

VirtualBox is a hosted hypervisor, which means it runs as an application on top of an existing operating system, not as a special kernel that is booted before the first regular operating system starts1. VirtualBox supports a large number of guest operating systems, including Windows, Linux, Solaris, OS/2, and OpenBSD1. VirtualBox does not require dedicated shared storage, as it can store virtual machine disk images locally on block devices of the virtualization host, or on network shares, or on iSCSI targets1. VirtualBox provides both a graphical user interface (GUI) and command line tools (VBoxManage) to administer virtual machines1. VirtualBox is available for Windows, Linux, macOS, and Solaris hosts1, and does not require the source code of the currently running Linux kernel to be available. References:

• Oracle VM VirtualBox: Features Overview

 Packer is a tool that automates the creation of identical machine images for multiple platforms from a single source configuration. Packer works by creating an instance based on a source image, which is a pre-existing image that serves as a starting point. Packer then connects to the instance through a network connection, such as SSH or WinRM, and runs various commands and scripts to install and configure software within the instance. Packer then shuts down the instance and creates a new system image from it, which can be used to launch new instances. Packer supports many platforms, such as AWS, Azure, VMware, Docker, and others. Packer does not install any software or run any daemon within the target image, nor does it periodically connect to the running instances to re-apply the template. Packer also does not modify the source image directly, but creates a new image from the modified instance. References:

• Packer by HashiCorp
• HashiCorp Packer - Build Automated Machine Images
• Introduction | Packer | HashiCorp Developer

Sparse images are a type of virtual disk images that grow in size as data is written to them, but do not shrink when data is deleted from them. Sparse images may consume an amount of space different from their nominal size, which is the maximum size that the image can grow to. For example, a sparse image with a nominal size of 100 GB may only take up 20 GB of physical storage if only 20 GB of data is written to it. Sparse images allocate backend storage at the first usage of a block, which means that the physical storage is only used when the virtual machine actually writes data to a block. This can save storage space and improve performance, as the image does not need to be pre-allocated or zeroed out.

Sparse images are not automatically shrunk when files within the image are deleted, because the virtual machine does not inform the host system about the freed blocks. To reclaim the unused space, a special tool such as virt-sparsify1 or qemu-img2 must be used to compact the image. Sparse images can be used with both full virtualization and paravirtualization, as the type of virtualization does not affect the format of the disk image. Sparse images are not automatically resized when their maximum capacity is about to be exceeded, because this would require changing the partition table and the filesystem of the image, which is not a trivial task. To resize a sparse image, a tool such as virt-resize3 or qemu-img2 must be used to increase the nominal size and the filesystem size of the image. References: 1 (search for “virt-sparsify”), 2 (search for “qemu-img”), 3 (search for “virt-resize”).

The purpose of the kubelet service in Kubernetes is to run containers on the worker nodes according to the Kubernetes configuration. The kubelet is an agent or program that runs on each node and communicates with the Kubernetes control plane. It receives a set of PodSpecs that describe the desired state of the pods that should be running on the node, and ensures that the containers described in those PodSpecs are running and healthy. The kubelet also reports the status of the node and the pods back to the control plane. The kubelet does not manage containers that were not created by Kubernetes. References:

• Kubernetes Docs - kubelet
• Learn Steps - What is kubelet and what it does: Basics on Kubernetes

The default path to the Docker daemon configuration file on Linux is /etc/docker/daemon.json. This file is a JSON file that contains the settings and options for the Docker daemon, which is the service that runs on the host operating system and manages the containers, images, networks, and other Docker resources. The /etc/docker/daemon.json file does not exist by default, but it can be created by the user to customize the Docker daemon behavior. The file can also be specified by using the --config-file flag when starting the Docker daemon. The file must be a valid JSON object and follow the syntax and structure of the dockerd reference docs12. References:

• Docker daemon configuration file - Medium3
• Docker daemon configuration overview | Docker Docs4
• docker daemon | Docker Docs5

The virt-diff command-line tool can be used to list the differences between files in two virtual machines or disk images. The output shows the changes to a virtual machine’s disk images after it has been running. The command can also be used to show the difference between overlays1. To specify two guests, you have to use the -a or -d option for the first guest, and the -A or -D option for the second guest. For example: virt-diff -a old.img -A new.img1. Therefore, the correct command to list all differences between the disk images vm1-snap.img and vm1.img is: virt-diff -a vm1-snap.img -A vm1.img. The other commands are not related to finding differences between disk images. virt-delta is a tool to create delta disks from two disk images2. virt-cp-in is a tool to copy files and directories into a virtual machine disk image3. virt-cmp is a tool to compare two files or directories in a virtual machine disk image4. virt-history is a tool to show the history of a virtual machine disk image5. References:

• 21.13. virt-diff: Listing the Differences between Virtual Machine Files …
• 21.14. virt-delta: Creating Delta Disks from Two Disk Images …
• 21.6. virt-cp-in: Copying Files and Directories into a Virtual Machine Disk Image …
• 21.7. virt-cmp: Comparing Two Files or Directories in a Virtual Machine Disk Image …
• 21.8. virt-history: Showing the History of a Virtual Machine Disk Image …

Libvirt uses XML files to store configuration data for objects in the libvirt API, such as domains, networks, storage, etc. This allows for ease of extension in future releases and validation of documents prior to usage. Libvirt does not use any of the other file formats listed in the question. References:

• libvirt: XML Format
• LPIC-3 Virtualization and Containerization: Topic 305.1: Virtualization Concepts and Theory

 Nested page table extensions, such as Intel Extended Page Table (EPT) or AMD Rapid Virtualization Indexing (RVI), are hardware features that facilitate the virtualization of memory. They allow the CPU to perform the translation of guest virtual addresses to host physical addresses in a single step, without the need for software-managed shadow page tables. This reduces the overhead and complexity of memory management for virtual machines, and improves their performance and isolation. Nested page table extensions do not directly affect the virtualization of other hardware components, such as network interfaces, host bus adapters, hard disks, or IO cache.

References:

• Second Level Address Translation - Wikipedia
• c - What is use of extended page table? - Stack Overflow
• Hypervisor From Scratch – Part 4: Address Translation Using Extended …

Cloud-init is a tool that processes configurations and runs through five stages during the initial boot of Linux VMs in a cloud. It allows users to customize a Linux VM as it boots for the first time, by applying user data to the instance. User data can include scripts, commands, packages, files, users, groups, SSH keys, and more. Cloud-init can also interact with various cloud platforms and services, such as Azure, AWS, OpenStack, and others. The purpose of cloud-init is to prepare the generic image of an laaS instance to fit a specific instance’s configuration, such as hostname, network, security, and application settings. References:

• Cloud-init - The standard for customising cloud instances
• Understanding cloud-init - Azure Virtual Machines
• Tutorial - Customize a Linux VM with cloud-init in Azure - Azure Virtual Machines

The WORKDIR instruction sets the working directory for any subsequent RUN, CMD, ENTRYPOINT, COPY and ADD instructions that follow it in the Dockerfile1. The RUN instruction executes commands in a new layer on top of the current image and commits the results2. The RUN cd command does not change the working directory for the next RUN instruction, because each RUN command runs in a new shell and a new environment3. Therefore, the file test is created in the root directory (/) of the container image, not in the /tmp directory. References:

• Dockerfile reference: WORKDIR
• Dockerfile reference: RUN
• difference between RUN cd and WORKDIR in Dockerfile

The FROM statement in a Dockerfile specifies the base image from which the subsequent instructions are executed1. The value of the FROM statement can be either an image name, an image name with a tag, or an image ID1. The image name can be either a repository name or a repository name with a registry prefix2. For example, ubuntu is a repository name, and docker.io/ubuntu is a repository name with a registry prefix2. The tag is an optional identifier that can be used to specify a particular version or variant of an image1. For example, ubuntu:focal refers to the image with the focal tag in the ubuntu repository2. The image ID is a unique identifier that is automatically generated when an image is built or pulled1. For example, sha256:9b0dafaadb1cd1d14e4db51bd0f4c0d56b6b551b2982b2b7c637ca143ad605d2 is an image ID3.

Therefore, the only valid value in the FROM statement among the given options is ubuntu:focal, which is an image name with a tag. The other options are invalid because:

• docker://ubuntu:focal is not a valid image name format. The docker:// prefix is used to specify a transport protocol, not a registry prefix4.
• registry:ubuntu:focal is not a valid image name format. The registry prefix should be a valid hostname or IP address, not a generic term2.
• file:/tmp/ubuntu/Dockerfile is not a valid image name format. The file: prefix is used to specify a local file path, not an image name5.
• http://docker.example.com/images/ubuntu-focal.iso is not a valid image name format. The http:// prefix is used to specify a web URL, not an image name5.

References:

• 1: Dockerfile reference | Docker Docs
• 2: docker - Using FROM statement in dockerfile - Stack Overflow
• 3: How to get the image id from a docker image - Stack Overflow
• 4: skopeo - Docker Registry v2 API tool - Linux Man Pages (1)
• 5: How to build a Docker image from a local Dockerfile? - Stack Overflow

Xen supports two types of guest systems: paravirtualized guests (PV) and fully virtualized guests (HVM).

• Paravirtualized guests (PV) are guests that have been modified to run on the Xen hypervisor. They use a special kernel that communicates with the hypervisor through hypercalls, and use paravirtualized drivers for I/O devices. PV guests can run faster and more efficiently than HVM guests, but they require the guest operating system to be ported to Xen and to support the Xen ABI12.
• Fully virtualized guests (HVM) are guests that run unmodified operating systems on the Xen hypervisor. They use hardware virtualization extensions, such as Intel VT-x or AMD-V, to create a virtual platform for the guest. HVM guests can run any operating system that supports the hardware architecture, but they incur more overhead and performance penalties than PV guests. HVM guests can also use paravirtualized drivers for I/O devices to improve their performance12.

The other options are not correct. Xen does not support foreign architecture guests (FA), emulated guests, or container virtualized guests.

• Foreign architecture guests (FA) are guests that run on a different hardware architecture than the host. For example, running an ARM guest on an x86 host. Xen does not support this type of virtualization, as it would require emulation or binary translation, which are very complex and slow techniques3.
• Emulated guests are guests that run on a software emulator that mimics the hardware of the host or another platform. For example, running a Windows guest on a QEMU emulator. Xen does not support this type of virtualization, as it relies on the emulator to provide the virtual platform, not the hypervisor. Xen can use QEMU to emulate some devices for HVM guests, but not the entire platform14.
• Container virtualized guests are guests that run on a shared kernel with the host and other guests, using namespaces and cgroups to isolate them. For example, running a Linux guest on a Docker container. Xen does not support this type of virtualization, as it requires the guest operating system to be compatible with the host kernel, and does not provide the same level of isolation and security as hypervisor-based virtualization56.

References:

• Xen Project Software Overview - Xen
• Xen ARM with Virtualization Extensions - Xen
• Xen Project Beginners Guide - Xen
• QEMU - Xen
• Docker overview | Docker Documentation
• What is a Container? | App Containerization | VMware

Libvirt supports creating and managing various types of virtual networks that can be used to connect virtual machines to each other or to the external network. One of the common types of virtual networks is the NAT-based network, which uses network address translation (NAT) to allow virtual machines to access the outside world through the host’s network interface. By default, libvirt creates a NAT-based network called ‘default’ when it is installed and started. This network appears as a standard Linux bridge device on the host system, named virbr0. The bridge device has an IP address of 192.168.122.1/24 and acts as a gateway and a DHCP server for the virtual machines connected to it. The bridge device also has iptables rules to forward and masquerade the traffic from and to the virtual machines. The virtual machines connected to the ‘default’ network have their own IP addresses in the 192.168.122.0/24 range and their own MAC addresses generated by libvirt. The virtual machines can communicate with each other, with the host, and with the external network through the bridge device and the NAT mechanism12.

The other statements in the question are false regarding networking with libvirt. Libvirt’s network functionality is not limited to connecting virtual machines to a physical network interface of the host system. Libvirt can also create isolated networks that do not have any connection to the outside world, or routed networks that use static routes to connect virtual machines to the external network without NAT3. Libvirt does not assign the same MAC address to all virtual machines and isolate their network interfaces at the link layer. Libvirt assigns a unique MAC address to each virtual machine and allows them to communicate with each other at the network layer4. Libvirt does not require a dedicated network interface that may not be used by the host system. Libvirt can share the host’s network interface with the virtual machines using NAT or bridging, or it can pass a physical network interface to a virtual machine exclusively using PCI passthrough5. Libvirt does not support exactly one virtual network and connect all virtual machines to it. Libvirt supports creating and managing multiple virtual networks with different names and configurations, and connecting virtual machines to different networks according to their needs6. References:

• libvirt: Virtual Networking
• libvirt: NAT forwarding (aka “virtual networks”)
• libvirt: Routed network
• libvirt: MAC address
• libvirt: PCI passthrough of host network devices
• [libvirt: Network XML format]